# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Single LOP is enough?
From: Bill Lionheart
Date: 2020 Sep 15, 22:01 +0100

```Of course if you could measure the azimuth accurately (eg on land) as
well as the altitude you would be on (one of) the intersection(s) of
the isoazimuth and the circle of position. Summary of discussion we
had here earlier this year (and the paper I have not finished writing)
"Isoazmuth curves can be surprisingly strange".

Bill

On Tue, 15 Sep 2020 at 21:17, Frank Reed  wrote:
>
> The key detail here: that azimuth that you see in the intercept method is
itself because it can have any value, dependent on the DR or AP or other
position that you feed into the calculation process. We don't have any means
of observing azimuths with great accuracy, but if we did, we could use them
for celestial position fixes.
>
> Let's imagine a super-compass enabling us to observe the azimuth of a star
to the nearest tenth of a minute of arc. Typical real compasses can get you
the azimuth to the nearest degree under good conditions and often worse. So
this super-compass would be on the order of 500 to 1000 times better at
measuring azimuths than anything we have today.
>
> Now observe the Sun with your (common) sextant and also your super-compass.
You get an altitude of, let's say, 60°15.5' (after applying altitude
corrections), and from your super-compass you get an azimuth of perhaps
175°12.0'. Then you look up the Sun's astronomical data, and you select and
arbitrary position near where you think you are to use as an "AP". From that
AP you calculate that the Moon's altitude should be 60°10.0' and it's azimuth
should be 175°09.5'. That tells us that our vessel is 5.5 nautical miles
towards the Sun, and it is also some miles (there's a little math involved)
to the left of the arbitrary AP (to the left when facing the Sun). With those
two observed pieces of information, we could fix our position. But there are
no super-sextants, at least not in commercial production.
>
> There's a general principle at work here. We want two numbers out of our
navigation process: latitude and longitude (or some equivalent x, y
coordinates). To get two quantities out, we need to feed two observed
quantities in. In normal celestial navigation, we observe two altitudes to
get latitude and longitude. With super-compass celestial navigation, we could
observe one altitude and one azimuth at the same time to get latitude and
longitude. Two in, two out.
>
> Frank Reed
>
> View and reply to this message
```
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